JPH0595414A - Cable disconnection detecting method - Google Patents

Abstract

PURPOSE:To detect the disconnection fault of a telephone circuit from a telephone exchange side without troubling a subscriber. CONSTITUTION:A capacitance at the normal time of cables L1, L2 to be tested is measured and recorded, and thereafter, when the disconnection of the cable is detected, the capacitance of the cable is measured, and by comparing it with the capacitance in a normal time, the disconnection of the cable is detected. A voltage measuring circuit is provided through a reference capacitor CR, a DC power source B and switches SW7, SW8. After the cable and the reference capacitor are charged by the DC power source, the cable and the reference capacitor which are charged are connected in opposite polarities, a voltage after charge is cancelled by the opposite polarity connection is measured by a voltage measuring circuit, and from a measured voltage, the capacitance of the cable is derived.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for detecting a disconnection of a subscriber telephone line on a telephone exchange side.

[0002]

2. Description of the Related Art Conventionally, a test device attached to a telephone exchange has been used to test a subscriber telephone line such as insulation degradation, short circuit, and crossed lines.

[0003]

In this case, these tests need to be performed on a daily basis as maintenance. In addition, in order to perform the tests without the trouble of the subscriber, it is necessary to perform the tests when the line is not used. As described above, the test is limited to the state in which the terminal is open, that is, the state in which the DC loop is open, so that it is not possible to determine whether the disconnection or the normal line non-use state. Therefore, the disconnection is to be discovered when the subscriber in question uses the telephone, and it has been desired that the disconnection be discovered in advance on the telephone exchange side for the sake of circuit maintenance.

SUMMARY OF THE INVENTION An object of the present invention is to provide a cable disconnection detecting method capable of detecting a disconnection failure of a telephone line from a telephone exchange side without bothering a subscriber.

[0005]

Means for Solving the Problems That is, according to the present invention, after measuring and storing the normal capacitance of a cable under test, the capacitance of the cable under test is measured when a cable break is detected, In the cable disconnection detection method for detecting cable disconnection by comparing with the electrostatic capacity at the time, a reference capacitor, a DC power supply, and a voltage measurement circuit are provided, and the cable to be tested and the reference capacitor are charged by the DC power supply. After that, the charged cable under test and the reference capacitor are connected in reverse polarity, and the voltage after charge cancellation due to the connection in the reverse polarity is measured by the voltage measuring circuit, and the electrostatic charge of the cable under test is measured from the measured voltage. There is a cable breakage detection method for obtaining the capacity.

[0006]

In the cable disconnection detection method thus constructed, first, in the case of detecting the insulation failure of the telephone line, the DC power supply is connected to the circuit in which the cable under test and the reference capacitor are connected in parallel through the series resistor. In the state of
Measure the voltage across the reference capacitor. In this case, if the insulation of the cable under test is degraded, the reference capacitor is charged with a voltage that is obtained by dividing the power supply voltage by the series resistance and the insulation resistance fault resistor, so the charging voltage across the reference capacitor is The voltage becomes lower than the power supply voltage, and the insulation failure of the cable under test can be detected.

Next, in the case of detecting the disconnection of the telephone line, in the state where the cable under test and the reference capacitor are charged by the DC power source, respectively, the combined capacitor of the cable under test and the reference capacitor is reversely connected. Voltage V
e, that is, the difference voltage Ve and the power supply voltage V and the capacitance C of the reference capacitor when the charges of both capacitors are cancelled.
The capacitance CX of the cable under test is calculated from R and Ask in. In this case, the capacitance CX of the cable under test in a normal state without disconnection is obtained in advance, and the capacitance CX of the cable under test when measured later is the capacitance CX in the normal state previously measured. When it is smaller, it can be determined that the wire is broken.

[0008]

As a result, the present invention has the effect that the disconnection failure of the telephone line can be easily found from the telephone exchange side without bothering the subscriber.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the structure of an embodiment of the present invention will be described with reference to the drawings. The DC power source B has resistors R1 and R2 at both ends thereof.
And the cables under test L1 and L2 of the telephone line are connected via the switches SW1 and SW2, and the cables under test L1 and L2 are connected.
The reference capacitor CR is connected between the two ends via the switches SW3 and SW4, and the reference capacitor CR is reversely connected via the switches SW5 and SW6 between the both ends of the series circuit of the DC power source B and the resistors R1 and R2. The reference capacitor CR is connected to a voltage measuring circuit (not shown) through switches SW7 and SW8 at both ends thereof.

Next, the operation of this embodiment will be described.
In the cable disconnection detection circuit configured in this way,
First, before measuring the capacitance, the cable L1 to be tested,
Switches SW1, SW2, SW3 for L2 insulation test
, SW4 are closed as shown in FIG. 1, a charging current flows from the DC power source B through the resistors R1 and R2 to the reference capacitor CR for measurement and the cables L1 and L2 under test. After charging is completed, the switches SW1, SW2, SW3, and S as shown in FIG.
W4 is opened and switches SW7 and SW8 are closed, and the voltage across the reference capacitor CR is measured. If the insulation condition of the cables L1 and L2 under test is good, the voltage across the cables L1 and L2 under test and across the reference capacitor CR becomes equal to the voltage V of the DC power supply B. If the insulation is degraded, a DC current will flow in the closed circuit formed by the DC power supply B and the resistances R1 and R2 and the fault resistance RX between the cables under test L1 and L2, and the voltage of the DC power supply B will cause a series resistance. R1
, R2 minus the voltage drop appears across the reference capacitor CR.

As a result, the fault resistance RX between the cables L1 and L2 to be tested, that is, the insulation resistance RX of the cables L1 and L2 to be tested, is assumed to be Ve at the voltage across the reference capacitor CR and V at the DC power supply B. , Is given by the following formula. If the insulation resistance RX is equal to or lower than the reference value, it means that the insulation is defective, and an alarm or the like is taken. At the same time, the next disconnection test is stopped. The energization / measurement shown in FIGS. 1 and 2 can be performed in an inverted state as shown in FIGS. 3 and 4.

Next, when the disconnection of the telephone line is detected, as shown in FIG. 5, the switches SW1, SW2, SW5 and S are connected.
Close only W6 to charge the reference capacitor CR for measurement and the cables L1 and L2 to be tested, and after charging,
As shown in FIG. 6, the switches SW1, SW2, SW5,
When SW6 is opened and only the switches SW3 and SW4 are closed, the reference capacitor CR and the cables L1 and L2 to be tested are connected, but since the charging voltage has the opposite polarity, only the charge difference remains. That is, the capacitance of the reference capacitor CR is CR, the capacitances of the cables under test L1 and L2 are Cx,
When the voltage of the DC power source B is V, the charge stored in the reference capacitor CR is QR, and the charge stored in the cables L1 and L2 under test is Qx, Qx is given by the following equation. Qx = CxV QR = CRV As shown in FIG. 6, when the reference capacitor CR and the cables under test L1 and L2 are connected in opposite polarities, their respective charges are canceled out and a difference remains. On the other hand, the capacity of the combined capacitor is the sum of CR and Cx, so the voltage Ve across the finally combined capacitors is given by the following equation. Therefore, the electrostatic capacitance Cx of the cables L1 and L2 under test is given by the following equation. In this case, when the cables to be tested L1 and L2 are broken, the electrostatic capacitance CX of the cables to be tested L1 and L2 is reduced, and thus the cables to be tested L1 and L2 are
2) The capacitance CX obtained in the normal state is stored in a storage device, for example, a storage device such as a flexible disk using a personal computer, etc., and the capacitance CX newly obtained in the test is stored in the normal state. When the newly obtained electrostatic capacitance CX is smaller than the stored normal electrostatic capacitance CX as compared with the electrostatic capacitance CX, it is possible to determine that the wire is broken. A personal computer can be used as the arithmetic circuit. In that case, a flexible disk device can be used as a storage device to store a large amount of data, and a personal computer can be used as the voltage measurement circuit. It is possible to use a voltmeter equipped with an interface for measuring instruments such as an analog / digital conversion board or GP-IB that can be incorporated in the.

[Brief description of drawings]

FIG. 1 is a cable disconnection detection circuit diagram at the time of energization when an insulation failure is detected.

FIG. 2 is a cable disconnection detection circuit diagram at the time of measurement when insulation failure is detected.

FIG. 3 is a circuit diagram of a cable disconnection detection circuit at the time of reversal energization when an insulation defect is detected.

FIG. 4 is a cable disconnection detection circuit diagram at the time of measurement when insulation failure is detected.

FIG. 5 is a cable disconnection detection circuit diagram during charging when disconnection is detected.

FIG. 6 is a circuit diagram of a cable breakage detection circuit at the time of short circuit when a breakage is detected.

FIG. 7 is a cable disconnection detection circuit diagram at the time of measurement when disconnection is detected.

FIG. 8 is a cable disconnection detection circuit diagram before disconnection detection.

[Explanation of symbols]

 B DC power supply R1 resistance R2 resistance CR reference capacitor SW1 to SW8 switches

Claims (1)

[Claims] 1. The capacitance of the cable under test is measured and stored, and then the capacitance of the cable under test is measured when a cable break is detected and compared with the capacitance during normal operation. In a cable disconnection detection method for detecting a cable disconnection, a reference capacitor, a DC power supply, and a voltage measuring circuit are provided, and after charging the cable under test and the reference capacitor with the DC power supply, the cable under test after charging and A cable disconnection characterized in that a reference capacitor is connected in reverse polarity, the voltage after charge cancellation due to connection in the reverse polarity is measured by the voltage measuring circuit, and the capacitance of the cable under test is determined from the measured voltage. Detection method.